This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. RNA polymerase II (Pol II) is responsible for synthesizing all the mRNA in eukaryote. Before an mRNA is made, a preinitiation complex (PIC) composed of over 50 proteins is nucleated around PolII to orchestrate promoter melting and transcription start site selection. Knowing the molecular architecture of PIC is critical to understand the molecular mechanism of the transcription as well as transcriptional regulation. In order to achieve this goal, we have recently assembled a mini-PIC system consisting of Pol II, TFIIB, TFIIF, TBP and promoter, which represent the essential core components of PIC.